Welcome to Connect, @manveen.
My dad didn't have a colostomy bag, so I don't have first-hand experience. But I did an Internet search and found very detailed information about leaks on this website: https://www.veganostomy.ca/ostomy-leaks-tips/
Here's an excerpt that may pertain to your situation:
"On a two-piece appliance, there’s always a very small risk that you can get leaks where the pouch connects to the wafer via the flange (called a coupling). It’s important to make sure that your mechanical coupling snaps together and is locked in place (if your pouch has that feature). You can give it a little tug to make sure that it’s secure. If you’re using an adhesive coupling, make sure that the surface you are sticking your bag to is clean and free of any moisture. You’ll also want to make sure that the adhesive is smoothed out and that there are no bubbles or creases in it."

Here's further information from Mayo Clinic about "Adapting to life after colostomy, ileostomy or urostomy" http://mayocl.in/2mb2dvk

I'm tagging @ilene1 @user_cha5e73f6 @soul @mkat5955 to see if they have any advice about leaky colostomy bags.
Manveen, do you live close to your mother?